The present invention relates generally to switching devices. More specifically, the present invention relates to improved packaging and circuit integration for electromagnetic devices, such as reed switches and electromagnetic devices such as reed relays.
Electromagnetic relays have been known in the electronics industry for many years. Such electromagnetic relays include the reed relay which incorporates a reed switch. A reed switch is a magnetically activated device that typically includes two flat contact tongues which are merged in a hermetically sealed glass tube filled with a protective inert gas or vacuum. The switch is operated by an externally generated magnetic field, either from a coil or a permanent magnet. When the external magnetic field is enabled, the overlapping contact tongue ends attract each other and ultimately come into contact to close the switch. When the magnetic field is removed, the contact tongues demagnetize and spring back to return to their rest positions, thus opening the switch.
Reed switches, actuated by a magnetic coil, are typically housed within a bobbin or spool-like member. A coil of wire is wrapped about the outside of the bobbin and connected to a source of electric current. The current flowing through the coil creates the desired magnetic field to actuate the reed switch within the bobbin housing. Some applications of reed devices require the switch to carry signals with frequencies in excess of 500 MHz. For these applications, a ground shield conductor, commonly made of copper or brass is disposed about the body of the reed switch. The ground shield conductor is commonly in a cylindrical configuration. The shield conductor resides between the reed switch and the bobbin housing to form a co-axial high frequency transmission system. This co-axial system includes the outer shield conductor and the switch lead signal conductor co-axially through the center of the reed switch. The ground shield conductor is employed to contain the signal through the switch conductor in order to maintain the desired impedance of the signal path.
Currently available reed devices are then incorporated into a given circuit environment by users. For application at higher frequencies, a reed switch device must be ideally configured to match as closely as possible the desired impedance requirements of the circuit in which it is installed.
Within a circuit environment, a co-axial arrangement is preferred throughout the entire environment to maintain circuit integrity and the desired matched impedance. As stated above, the body of a reed switch includes the necessary co-axial environment. In addition, the signal trace on the user""s circuit board commonly includes a xe2x80x9cwave guidexe2x80x9d where two ground leads reside on opposing sides of the signal lead and in the same plane or a xe2x80x9cstrip linexe2x80x9d where a ground plane resides below the plane of the signal conductor. These techniques properly employed provide a two-dimensional, co-axial-like environment which is acceptable for maintaining the desired impedance for proper circuit function.
However, the reed switch device must be physically packaged and electrically interconnected to a circuit board carrying a given circuit configuration. It is common to terminate the shield and signal terminals to a lead frame architecture and enclose the entire assembly in a dielectric material like plastic for manufacturing and packaging ease. These leads may be formed in a gull-wing or xe2x80x9cJxe2x80x9d shape for surface mount capability. The signal leads or terminals exit out of the reed switch body and into the air in order to make the electrical interconnection to the circuit board. This transition of the signal leads from plastic dielectric to air creates an undesirable discontinuity of the protective co-axial environment found within the body of the switch itself. Such discontinuity creates inaccuracy and uncertainty in the impedance of the reed switch device. As a result, circuit designers must compensate for this problem by specifically designing their circuits to accommodate and anticipate the inherent problems associated with the discontinuity of the protective co-axial environment and the degradation of the rated impedance of the reed switch device. For example, the circuit may be tuned to compensate for the discontinuity by adding parasitic inductance and capacitance. This method of discontinuity compensation is not preferred because it complicates and slows the design process and can degrade the integrity of the circuit. There is a demand to reduce the need to tune the circuit as described above. The prior art uses a structure of carefully designed vias, which are expensive and difficult to manufacture, to control the impedance from the relay to the board transition.
In view of the foregoing, there is a demand for a reed switch device that includes a controlled impedance environment through the entire body of the package to the interconnection to a circuit. There is a particular demand for a reed switch device to be compact and of a low profile for installation into small spaces and for circuit board stacking. There is further a demand for reed switch devices that are of a surface mount configuration to optimize the high frequency of the performance of the system. Further, there is a demand for a reed switch device that can reduce the need to tune a circuit to compensate for an uncontrolled impedance environment. Also, there is a demand for a reed switch device that has a small footprint and is of a standard shape and configuration for simplified manufacture and installation.
The present invention preserves the advantages of prior art electromagnetic switch devices, such as reed relays. In addition, it provides new advantages not found in currently available switching devices and overcomes many disadvantages of such currently available devices.
The invention is generally directed to the novel and unique reed switch device with particular application in effectively interconnecting a reed switch device to a circuit on a circuit board in a low profile configuration. The reed switch package of the present invention enables the efficient and effective interconnection to a circuit board while being in an inexpensive construction.
A new electromechanical device is provided that mounts to a relay substrate to form a low profile, board mountable reed relay. A portion of the reed relay extends through an aperture in the relay substrate. The substrate includes a series of electrical contacts, such as solder balls array (BGA), land grid array (LGA), column grid array (CGA), or pin grid array (PGA), mounted to the same side of the substrate that the relay mounts to electrically connect to the main circuit card. The reed relay itself is directly electrically connected to the electrical contacts via signal traces and additional electrical traces located on the bottom of the relay substrate which connect to the relay""s shielding. These additional traces are routed in a parallel position on both sides of the signal traces to provide a co-planar wave guide to maintain the desired impedance of the signal path. The reed relay substrate is mounted into a cut-out in the main circuit board in an inverted manner so that a portion of the reed relay not within the substrate recess sits within a cut-out in the main circuit board. As a result, the reed relay component is recessed below the surface of the main circuit board resulting in an overall low profile circuit board.
It is therefore an object of the present invention to provide a compact, low profile reed switch package.
It is an object of the present invention to provide a reed switch device with a controlled impedance environment throughout the entire package.
It is a further object of the present invention to provide a reed switch package that is easily matched to the impedance of an existing circuit environment.
Another object of the present invention is to provide a reed switch package that is capable of efficiently conducting high frequency signals.
It is a further object of the present invention to provide a reed switch package that is inexpensive to manufacture by not requiring the use of plated through hole vias.
It is yet a further object of the present invention to provide a reed switch package with a small footprint.
Another object of the present invention is to provide a reed switch package that can be easily surface mounted to a main circuit board.